1. Field of the Invention
The present invention relates generally to packaging and, more specifically, to a laminated chip scale package formed of a die and a micromachined silicon wafer segment or blank bonded to the active surface of the die. The package may be executed at the wafer level.
2. State of the Art
Packaging for semiconductor dies takes a variety of forms. Transfer-molded packages, comprising a filled polymer encompassing a die wire-bonded or otherwise electrically connected to a lead frame, are prevalent in today's market. Other types of packaging, such as preformed ceramic or even metal packages, in which die are secured and then placed in electrical communication with package conductors, are also employed. Similarly, so-called "glob-top" encapsulation (with an epoxy, silicone gel, polyimide, and other organic, plastic and the like) of dies mounted and usually wire-bonded to a substrate such as a printed circuit board is also widely employed. Underfill of a flip-chip mounted to a substrate is also known in the art; such procedure may be followed by glob-topping the assembly. It has also been suggested to hermetically protect integrated circuits (dies) with a silicon-containing ceramic layer; see U.S. Pat. No. 5,481,135.
All of the foregoing packaging schemes, however, suffer from one or more deficiencies. For example, plastic packaging with lead frames and wire bonds is a multi-step process, wherein a defectively-performed individual step may compromise the quality of the end product if any individual step is deficient. Moreover, matching of the coefficients of the thermal expansion (CTE) of die, lead frame and encapsulant is virtually impossible, requiring additional structural features or process steps to accommodate thermally-induced stresses. Further, plastic packages do not provide a hermetic seal, e.g., are not effective to prevent the ingress of moisture to the package interior. Ceramic and metal packages provide hermetic protection, but are expensive and require as many if not more process steps as a transfer-molded plastic package.
Glob-topping a die is relatively easy, but the resulting protection for the die and conductors is less than robust in comparison to other alternatives. Underfilling of a flip-chip connection followed by glob-topping is process-intensive and suffers from quality control constraints due to an inability to verify the integrity of the underfill. With the exception of ceramic and metal packages, all of the current packaging alternatives, including application of a ceramic layer to the surface of a die, may fail to provide a hermetic seal of any quality or repeatability for the die. Moreover, most current die packages are far more massive in both lateral and vertical extent than the die itself, thus absorbing valuable "real estate" on the substrate or other carrier to which the die is mechanically attached and electrically connected, and increasing the size of the external circuit in which the die is incorporated.
So-called "direct" die attach (DDA) or "discrete" or "direct" die connect (DDC) configurations have been developed to facilitate the direct connection of one or more unpackaged or "bare" die to the next level of packaging. Such schemes may simply use a variation of a flip-chip die attach, may actually employ an intermediate substrate carrying more than one die to effect the connection to a carrier, or may use an "edge-connect" arrangement to mechanically and electrically connect vertically-oriented die to a carrier. These approaches, while meritorious from a space-saving standpoint, subject the bare die itself to potential damage during handling and execution of the die-connect, as the relatively delicate active surface of the die, with its active and passive devices as well as a myriad of conductive traces, is placed at risk. Moreover, configuring dies with a bond pad arrangement suitable for an edge-connect is no small feat, given the necessity of placement of all of the external connections for accessing the die at one edge thereof. Thus, some edge-connect approaches are a compromise of a true direct die connect by virtue of using a larger, conductor-carrying film or board to effect the edge connections.
In summary, state-of-the art packaging schemes fail to achieve reliable, substantially hermetic die protection on a size scale of the die itself, which the inventors herein term a "chip scale" package. Moreover, state-of-the-art packaging schemes fail to provide a technique to reliably effectuate a chip scale DDC with hermetic die protection.